The present invention is generally directed to diamond coatings. More particularly, the present invention is directed to diamond formation on a WCxe2x80x94Co (tungsten carbide-cobalt-carbon) substrate using multiple lasers.
The concept that diamond can be grown exclusively within its thermodynamic stability region is no longer valid. (Reference may be had to, for example, A. Badzian, T. Badzian, Int. J. of Refractory Metals and Hard Materials 15 (1997) 3.) The search for novel approaches to diamond synthesis, different from HP/HT and CVD operations, continues despite opinions that these two classical methods are sufficient for most applications. The new research is surrounded by the uncertainty in the growth mechanisms. This is the situation with the recent demonstrations of a laser induced process conducted in the open air (see, for example, P. Mistry, M. C. Turchan, S. Liu, G. O. Granse, T. Baurman, M. G. Shara, Innovations in Materials Research 1 (1996)193) and on hydrothermal growth (see, for example, X-Z Zhao, R. Roy, K. A. Cherian, A. Badzian, Nature 285 (1997) 513). The chemical reaction paths are unknown for these two new processes, and an explanation does not seem to be forthcoming. Diamond coatings on WCxe2x80x94Co cutting tool inserts by the laser process are factual and have been successfully tested for wear resistance. Nevertheless, a plausible growth hypothesis has yet to be presented.
Accordingly, it is an object of the present invention to define a method of adhesion of a diamond coating on a substrate.
It is a further object of the present invention to define such a method as it applies between the diamond coating and a WCxe2x80x94Co substrate.
Still a further object of the present invention is apply the defined method to the requirements of electron field emission.
The process of applying a diamond coating to a WCxe2x80x94Co substrate to prepare includes the steps of employing a plasma and a variety of interactions from a multiple laser system using WCxe2x80x94Co substrates. The process is conducted in open air and does not involve hydrogen. Structural characterization of the diamond coatings, which have exceptional adhesion to cutting tool inserts, indicates a cubic diamond structure.
The coatings on the WCxe2x80x94Co substrate are typically between 25 and 40 xcexcm thick. The average crystal size is between 10 and 20 xcexcm. Various methods of confirming the cubic diamond structure of the coatings have been employed. The adhesion of the diamond coating to the substrate is very strong. An electron microprobe analysis shows tungsten and cobalt atoms incorporated into the film and a layer depleted in cobalt exists at the diamond-WCxe2x80x94Co interface. Particulates of W/Co/C alloy are spread over the top surface, apparently formed by condensation from the vapor phase of metal-containing molecules. Carbon is confirmed as being the main component of the surface layer.
Electron field emission current densities, useful for flat panel displays of 6 mA/cm2 at an applied voltage of 3000 V for a film-anode distance of 20 xcexcm has been measured.